1. Field of the Invention
The present invention relates to a semiconductor device having a mold package structure (ball giid array package or land grid array package) obtained by sealing a semiconductor chip loaded on a frame of an organic material such as glass epoxy resin with resin by transfer molding.
2. Description of the Prior Art
In a semiconductor device having a mold package structure (BGA or LGA) employing a frame of an organic material such as glass epoxy resin, a semiconductor chip loaded on the frame is sealed with resin by transfer molding.
The frame is previously formed with pads connected with the semiconductor chip through inner bumps or by flip chip bonding, pads forming external connection electrodes and wiring patterns coupling the pads with each other.
FIGS. 11 and 12 show structures of semiconductor chips loaded on frames respectively. FIG. 11 shows a flip chip bonding structure obtained by directing the active surface of a semiconductor chip 4 downward (face down bonding) to wiring patterns 6 provided on the surface of a frame 2 and electrically connecting pad electrodes (not shown) of the semiconductor chip 4 with the wiring patterns 6 through inner bumps 5. The semiconductor chip 4 and the inner bumps 5 are sealed with a package 1.
FIG. 12 shows a wire bonding structure obtained by directing the active surface of a semiconductor chip 4 upward (face up bonding) to wiring patterns 6 provided on the surface of a frame 2 and fixing the semiconductor chip 4 to the frame 2 with a die bonding material 8 while electrically connecting pad electrodes (not shown) of the semiconductor chip 4 with the wiring patterns 6 through metal thin wires 7. The semiconductor chip 4 and the metal thin wires 7 are sealed with resin 1. After the semiconductor chip 4 is sealed with resin, external connection electrodes are formed on the rear surface of the frame 2 in each of the flip chip bonding structure and the wire bonding structure. The external connection electrodes may be formed by wires of the frame 2 themselves, or balls consisting of solder or the like. After formation of the external connection electrodes, the frame 2 is divided into a fragment with a mold or a laser beam, thereby completing a semiconductor device sealed with resin.
In the conventional semiconductor device having the aforementioned mold package structure, the overall loaded surface of the chip 4 is sealed with resin by transfer molding in an area equivalent to that of the frame 2.
If the ratio of the area occupied by the semiconductor chip 4 to the total area of the frame 2 is small, however, the package is considerably warped as shown in FIG. 13 or 14. Thus, the package is restricted in size with respect to the semiconductor chip 4.
Particularly when the package is at least 15 mm square in size and has at least 250 external connection electrode pins, warpage of the package may exceed 0.1 mm depending on the chip size, to result in the following problems:
Warpage of the package directly correlates with the flatness of the external connection electrodes. If the package is remarkably warped, the external connection electrodes of the semiconductor device are not connected with wires of a printed board.
The resin employed for transfer molding remarkably hardens/shrinks as the thickness thereof increases. If the resin sealing the semiconductor device has a large thickness, therefore, the package is inevitably remarkably warped.
Also when the loaded surface of the semiconductor chip is not entirely sealed with resin in an area equivalent to that of the frame but only a chip area is sealed with resin, the flatness of the external connection electrodes is deteriorated due to warpage of the mold package.
This defect tends to occur when the employed frame is extremely thin (about 0.1 mm), conceivably because of winding or warpage of the frame partially exposed on the outside of the semiconductor chip area. In the structure of this mold package, the strength of the package itself is extremely reduced, to conceivably result in inconvenience when the package is mounted on a printed board or the like.